The present invention relates to a method for feeding lumber, especially in connection with a four-band saw, in order to separate and feed side boards. The invention also relates to an apparatus for working the method.
In four-band sawing the problem is how to separate the pair of side boards, sawed off from both sides of the log, in order to be further processed--for example trimmed.
In the previous art is known a method for separating side boards wherein the side boards are dropped in disorder onto a transverse conveyor to form two piles on both sides of the block. The separation of the boards before further processing is carried out for example by means of a separating pocket and a log hoist.
The drawback of the above described method is that the side boards leave the sawing station along the transverse conveyor in disarray, wherefore it is necessary to employ manpower and clearing equipment--a separating pocket and a log hoist--in order to separate the boards from each other and to feed them one by one for further processing. In the separating pocket the boards tend to turn the wrong side up, i.e. with their cant edge down, so that also swivelling equipment is required in the apparatus. Moreover, the log hoist may break boards and thus cause interruptions in the process. As a whole this kind of apparatus is complicated and susceptible to disturbance. It can be regarded as a hindrance to utilizing the full capacity of the four-band saw.
The Finnish patent application No. 800563 introduces a lumber feeding apparatus where it has been tried to eliminate the aforementioned drawbacks. This application relates to an apparatus where, for instance in the sawing position of a four-band saw, the side boards are transported between side supports along both sides of the block, in a trough on top of support rollers, until the sawing operation is completed. The support rollers are for a moment drawn out of the trough, so that the side boards fall into the two pockets located on both sides of the block between the side supports. In both pockets the boards are pressed against the other stationary pocket and simultaneously against the wall of the trough by means of a moving wall operated by a bellow device filled with pressurized air. Those boards in the pocket that are located against the adjustable wall are sucked into place by employing an underpressure a vacuum. The bellow device is loosened and the bottoms of the pockets opened, so that only those two side boards that are located against the stationary wall both fall into their respective compartments in the conveyor below. The conveyor is then shifted, and the remaining side boards are dropped into their conveyor compartments. The bottoms of the pockets are closed and the same operation phases are repeated with the following side boards.
An advantageous achievement of the above described apparatus is that for example the log hoist becomes unnecessary and the side boards can be placed directly onto the single conveyor. The drawback of the apparatus, however, is that it has a complex structure and therefore it is costly to manufacture. The reliability of the feeding device is also decreased because of the numerous phases of operation. In connection with an apparatus of this kind it is necessary to employ board swivelling means, because the side boards fall into the conveyor chambers arbitrarily. Moreover, the thickness of the lumber to be fed into the process sets certain limitations to the use of the apparatus.